The present invention relates to a needle guide in a sewing machine which is provided with a thread trimmer and a feeding device generating a relative feed movement between a workpiece and stitch forming elements.
In the German Gebrauchsmuster No. 76 05 072 U.S. Pat. No. 4,088,085 there is illustrated a sewing machine of a type in which the needle aperture is laterally moved in a timed relationship to the movement of the needle as to form a support for the downwardly moving needle thus preventing the needle from damaging the beak of the hook. In order to generate such lateral movements of the needle aperture, an expensive and complex drive mechanism is required. Due to the direction of the aperture jogging movement with respect to the angular extension of the hook shaft, this type of needle guide or support may not be easily applied with hooks having a differently arranged hook shaft as illustrated.
Generally, a sewing machine of the above-mentioned kind is equipped with a thread cutter terminating the sewing process. In order to achieve a cut of threads as close as possible at the workpiece, the thread cutter is arranged between the workpiece supporting plate and the rotary hook. Due to the constructive conditions in the known sewing machine, the described needle guide or support is arranged at a certain distance relatively to the beak of the hook. Furthermore, the described sewing machine is equipped with a feeding mechanism, which generates a continuous feeding movement in a multilateral direction. In a specific feed direction--i.e. as the workpiece is moved towards the beak of the hook--due to the action of the needle aperture a lateral deflection of the needle in a direction off the beak is rendered possible. This finally affects the loop seizing procedure, i.e. causes an unsafe stitch formation. So as to avoid interference while other feeding directions are performed, the described jogging movements of the needle aperture are shut off by means of a special control system.
A rotary hook of the aforementioned type is described in U.S. Pat. No. 3,120,204. To the rotating hook body there is screwed a needle guard formed with a surface positioning or guarding the needle. The needle guard is arranged so as to cooperate with the tip portion of the needle and thereby not avoiding a collision of the needle and the beak of the hook, while a feed movement of the workpiece in the direction towards the beak is produced. Additionally, the needle is exposed to frictional heat due to the high velocity of the needle guard contacting the needle each time at the instant of loop seizure. By the application of this type of rotary hook in a sewing machine of the aforementioned kind, the described difficulties in the form of unsafe stitch formation and damages of the needle or hook may not be eliminated.
Accordingly, it is a main object of the present invention to provide a sewing machine having a thread cutter with a needle guide or guard, which cooperates with the needle in a close position to the beak of the hook.
It is a further object of the present invention to create a needle guide, which is small in design without interfering with the thread cutter.
Another object of the present invention is to create a needle guide which is simple in construction and applicable independently of the angular arrangement of the hook shaft.
Still another object of the present invention is to create a needle guide which is economical to manufacture and easily to install in machines that are already in use in the field.